code: def test_hillclimb(self):
      # arrange
      initial_alignment = AlignmentInfo((0, 3, 2), None, None, None)
  
      def neighboring_mock(a, j):
          if a.alignment == (0, 3, 2):
              return {
                  AlignmentInfo((0, 2, 2), None, None, None),
                  AlignmentInfo((0, 1, 1), None, None, None),
              }
          elif a.alignment == (0, 2, 2):
              return {
                  AlignmentInfo((0, 3, 3), None, None, None),
                  AlignmentInfo((0, 4, 4), None, None, None),
              }
          return set()
  
      def prob_t_a_given_s_mock(a):
          prob_values = {
              (0, 3, 2): 0.5,
              (0, 2, 2): 0.6,
              (0, 1, 1): 0.4,
              (0, 3, 3): 0.6,
              (0, 4, 4): 0.7,
          }
          return prob_values.get(a.alignment, 0.01)
  
      ibm_model = IBMModel([])
      ibm_model.neighboring = neighboring_mock
      ibm_model.prob_t_a_given_s = prob_t_a_given_s_mock
  
      # act
      best_alignment = ibm_model.hillclimb(initial_alignment)
  
      # assert: hill climbing goes from (0, 3, 2) -> (0, 2, 2) -> (0, 4, 4)
      self.assertEqual(best_alignment.alignment, (0, 4, 4))
  
file_path: nltk/nltk/test/unit/translate/test_ibm_model.py
imports: import unittest
  from collections import defaultdict
  from nltk.translate import AlignedSent, IBMModel
  from nltk.translate.ibm_model import AlignmentInfo
label_desc: Use image node_id 11 for calling the TestIBMModel obj's underlying member method code with example usage: obj.test_hillclimb() and returns: set, prob_values, unknown, unknown